Gap at bottom of door



I'm in the process of re-painting my front door and adjusting the
glass pane in the door.

When I took off the bottom cover on the door I discovered yet another
trick the builder used to cut costs and rip me off.

There is A GAPING ONE INCH GAP between the bottom of the door and the
metal panel that it closes onto !!!

The plastic cover at the bottom of the door has served little more
than a visual finishing.
Cold and noise have obviously been coming in through that gap for
years.

I don't know what type of door it is metal/wood?
But whatever is the cheapest available, that's it! :(

I would like to close that one inch gap as best as possible.

Can anyone suggest the best method?

TIA
.